Modeling the Concentration Behavior of the Resistance and Thermopower of Percolation Composites (Conductor –HfC) Obtained in the Presence of a Binder

Abstract

We studied the percolation composites Si3N4-HfC in the HfC concentration range from 10 to 40 vol%, in which the conducting composite was located in a layer with a cross section b / t = 4 in an insulating shell of Si3N4, respectively. The layers were formed in the presence of rubber binders, carboxymethyl cellulose, or without a binder. Consolidation of the composite was carried out by hot pressing in a graphite mold. The simulation of the concentration dependence of resistance was carried out in accordance with the approximations of the McLachlan theory. The microstructure and phase composition of the composites were studied, a quantitative analysis of the images of the microstructure was carried out, as well as X-ray phase spectral microanalysis. Temperature dependences of resistance and TEMF were carried out in the temperature range from room temperature to 600°C. It was found that the fineness of the microstructure of the consolidated composites significantly depends on the type and presence of the binder. These differences determine the concentration dependence of the resistance, as well as the presence and sign of TEMF. A correlation was established between the anisotropy of the resistance value of the composite along and across the direction of hot pressing with the magnitude of TEMF, as well as the type of the used binder with the sign of TEMF. It is shown the Si3N4-HfC composition had a sign reversal depending on the temperature. In composites prepared without a binder, the level of thermoelectric power was close to zero